Scandium precursor for SC2O3 or SC2S3 atomic layer deposition

ABSTRACT

Described are precursor compounds and methods for atomic layer deposition of films containing scandium(III) oxide or scandium(III) sulfide. Such films may be utilized as dielectric layers in semiconductor manufacturing processes, particular for depositing dielectric films and the use of such films in various electronic devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/US2016/055067, filed on Oct. 1, 2016, the entire contents of which is hereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to scandium precursors for atomic layer deposition of films containing scandium(III) oxide, Sc₂O₃ or scandium (III) sulfide, Sc₂S₃. The scandium precursors, in liquid form and with relatively high thermal stability and relatively high vapor pressure, are conveniently sourced from amidinate-based ligand structures. The films are then employed in semiconductor manufacturing processes, particularly for depositing dielectric films and use of such films in various electronic devices.

BACKGROUND

Atomic layer deposition (ALD) has emerged as a popular technology for the preparation of highly conformal, ultra-thin films. More specifically, ALD has been employed for the deposition of electrically insulating materials with high dielectric constants (high-k dielectrics) as gate insulators in high-speed transistors as well as ultrathin gate interlayers in the integration of new channel materials.

Successful precursors for deposition are preferably volatile, thermally stable and highly reactive. Identifying new and more efficient compounds that satisfy these requirements remains challenging. With regards to high-k dielectric oxides based on Sc₂O₃, many current precursors lack such requirements suitable for ALD processing.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of various embodiments of the claimed subject matter will become apparent as the following Detailed Description proceeds, and upon reference to the Drawings, wherein like numerals designate like parts, and in which:

FIG. 1 indicates a combined Thermal Gravimetric Analysis (TGA) and Differential Scanning calorimetry trace of the amidinate type scandium precursor in accordance with the present disclosure;

FIG. 2 indicates a Thermal Gravimetric Analysis vapor pressure curve under isothermal conditions of the amidinate type scandium precursor in accordance with the present disclosure;

FIG. 3 indicates a Thermal Gravimetric Analysis (programmed heating) of the amidinate type scandium precursor herein versus Cp₃Sc(Cp=cyclopentadienyl), Sc(THD)₃(THD=2,2,6,6-tetramethyl-3,4-heptanedionato) and Sc(OiPr)₃(OiPr=isopropoxide).

FIG. 4 indicates a comparative Thermal Gravimetric Analysis of freshly distilled amidinate type scandium precursor herein compared to a sample of such precursor subjected to prolonged and sustained heating at 150° C. for one week.

Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications and variations thereof will be apparent to those skilled in the art.

DETAILED DESCRIPTION

The present disclosure is directed to scandium precursors suitable for atomic layer deposition (ALD) of films containing scandium(III) oxide, Sc₂O₃ or scandium (III) sulfide, Sc₂S₃. In an embodiment of the present disclosure the precursor is an amidinate type scandium precursor and has the following structural formula:

wherein R₁, R₂ and R₃ are selected from the group consisting of alkyls, allyls, aryls, heteroaryls, hydrogen, non-metals and metalloids and where R₁, R₂ and R₃ are different or the same. Accordingly, in the context of the present disclosure, the amidinate type scandium precursor herein may be identified as Sc(Amid-R₁, R₂, R₃)₃. Alternatively, one may identify the amidinate precursor herein as Sc(Amid-Et,Me)₃ in that situation where an ethyl group and methyl group serve as the source for the selection of R₁, R₂ and R₃.

Accordingly, R₁, R₂ and R₃ are preferably selected from alkyls, including methyl, ethyl and/or propyl group functionality. In one further preferred embodiment, the amidinate type scandium precursor herein may therefore have the following structure, which may be abbreviated herein as Sc(Amid-Me)₃:

The amidinate type scandium precursor herein is preferably prepared according to the following general scheme, where R₁, R₂ and R₃ may be as described above:

The amidinate type scandium precursors herein provide a very useful combination of dielectric (k) values, thermal stability and processing capability. Attention is directed to FIG. 1 which provides a Thermal Gravimetric Analysis (TGA) and Differential Scanning calorimetry analysis (DSC) for the amidinate type scandium precursor Sc(Amd-Et,Me)₃. As can be seen, the TGA curve shows what may be identified as a clean evaporation profile with near zero residue at a temperature of 210° C. (≤0.1% wt.). It may therefore be appreciated that the amidinate type scandium precursors herein are such that they indicate thermal stability (no breakdown of the structure) in the temperature range of 30° C. to 210° C., in the absence of any co-reactant.

The DSC curve in FIG. 1 indicates an endothermic transition centered around 67.2° C. which corresponds to the solid-liquid transition (melting) which occurs prior to the onset of evaporation. Accordingly, in the broad context of the present disclosure, it is contemplated that the amidinate type scandium precursors herein indicates a DSC melting temperature of 67.2° C., plus or minus 5° C. The heating rate in the DSC is preferably in the range of 5-10° C./minute. The TGA and DSC evaluation illustrated in FIG. 1 therefore confirms the ability to provide the amidinate type scandium precursors herein in liquid form as well as suitable evaporation characteristics for use in ALD processing.

FIG. 2 indicates a Thermal Gravimetric Analysis vapor pressure curve under isothermal conditions for the amidinate type scandium precursor Sc(Amid-Me, Et)₃. As can be seen, the precursor indicates a vapor pressure of 0.1 Torr at about 95° C. and a vapor pressure of 1.0 Torr at 130° C. It is therefore the case that the amidinate type scandium precursors herein indicate a vapor pressure of 0.1 Torr to 1.0 Torr over the temperature range of 95° C. to 130° C. Such vapor pressure characteristics are again now suitable for use of the precursors herein for ALD reactors.

FIG. 3 next indicates a Thermal Gravimetric Analysis (programmed heating) of the amidinate type scandium precursor herein versus Cp₃Sc(Cp=cyclopentadienyl), Sc(THD)₃(THD=2,2,6,6-tetramethyl-3,4-heptanedionato) and Sc(OiPr)₃(OiPr=ispropoxide). This comparison confirms that the amidinate type scandium precursors herein are relatively more volatile than the other identified scandium precursors, which other precursors also indicated decomposition before volatization appeared to take place, as indicated in part by the erratic behavior at the end of the TGA scan.

FIG. 4 indicates a comparative Thermal Gravimetric Analysis of the freshly distilled amidinate type scandium precursor (Sc(Amd-Me,Et)₃ herein compared to a sample of such precursor subjected to prolonged and sustained heating at 150° C. for one week. As can be observed, there is essentially no change in evaporation profiles which therefore confirms the thermal stability of the amidinate type scandium precursors disclosed herein.

As alluded to above, the amidinate type scandium precursors herein may be utilized for atomic layer deposition (ALD), which is a thin-film deposition technique based on the precursors herein which may react with a surface followed by removal of unreacted molecules, followed by introduction of a co-reactant, such as water or hydrogen sulfide (H₂S), which leads to thin film deposition of either Sc₂O₃ or Sc₂S₃. Accordingly, during a preferred ALD process a heated substrate (e.g. a substrate temperature in the range of 200° C. to 500° C.) can be repeatedly exposed to (a) the amidinate type scandium precursor herein; (b) a chamber purge to remove excess precursor plus any by-products; (c) a co-reactant; and (d) a final chamber purge to remove reaction by products. It is contemplated herein that films containing Sc₂O₃ or Sc₂S₃ may therefore now be formed having thicknesses of less than or equal to 300 Angstroms, or in the range of 5 Angstroms to 300 Angstroms.

The films containing Sc₂O₃ or Sc₂S₃ herein when combined with rare earth elements (Y, Gd, La) are further contemplated to produce ternary rare earth scandates of the formula (REScO₃ or REScS₃) where RE stands for rare earth. Such ternary scandates are contemplated to have thermal stabilities to 900° C. and dielectric k values of up to 22, which therefore make them suitable as gate insulators for in relatively high speed transistors as well as gate interlayer materials in the integration of new channel materials. In addition, the films herein containing Sc₂O₃ or Sc₂S₃ formed from the amidinate type scandium precursors herein are such that they can incorporate nitrogen at levels of 0.5 at. % to 10.0 at. %, which can be measured by X-ray photoelectron spectroscopy (XPS).

A semiconductor process flow may therefore utilize the films disclosed herein for formation of high-k metal gate transistors, for instance. For example, during a gate replacement process a film comprising the ternary scandates herein (Sc₂O₃ or Sc₂S₃) may be formed, e.g., using the scandium precursor herein, directly below the gate electrode to provide a gate dialelectric after dummy gate removal to improve channel performance. Any number of transistor types and/or formation process flows may benefit from a gate dialectric formed using the films disclosed herein, such as complementary metal-oxide-semiconductor (CMOS) transistor semiconductor devices having N-type or P-type configurations, whether configured with thin or thick gates, and with any number of geometries. Moreover, the resulting gate dialelectric herein may be used in various transistor devices including planar and non-planar configurations, e.g., finned transistor configurations such as tri-gate or FinFET devices, multi-gate devices, nanowire/nanoribbon devices, and so on.

The following examples pertain to further embodiments of the present disclosure and may comprise subject material such as a compound or process for forming a film, wherein the film is suitable for use in semiconductor manufacturing processes.

The general exemplary procedure is as follows, with the specific compound examples identified below: under a nitrogen atmosphere, 1.0 g (10 mmol) of the amidine in THF (20 mL) was deprotonated with n-BuLi (1.6 M/hexanes, 6.8 mL, 11 mmol) at 78° C. After the addition was completed, the mixture was warmed to room temperature and stirred for 1 hour. This solution was then added via cannula to a −78° C. flask containing solid ScCl₃(THF)3 (1.22 g, 3.33 mmol) and the mixture was allowed to slowly warm up overnight. The volatiles were vacuum removed and the residue extracted into hexanes (30 mL) and filtered. The colorless residue obtained was bulb-to-bulb distilled at 120-130° C. using a −78° C. receiving flask. The final complex was isolated as a white solid (m.p. 64-67° C. determined by DSC) at about 80% yield. Accordingly, in the broad context of the present disclosure, the yields herein of the subject amidinate type scandium precursors are clearly at a level of at least 50%, more preferably at least 60%, or at least 70%, as well as up to at least 80%. It may therefore be understood that the yields herein of the amidinate type scandium precursor may also be described as falling in the range of 50% to 80%, 60% to 80%, or 70% to 80%.

Example 1

According to this example there is provided a compound having the structural formula:

wherein R₁, R₂ and R₃ are selected from the group consisting of alkyls, allyls, aryls, heteroaryls, hydrogen, non-metals and metalloids and where R₁, R₂ and R₃ are different or the same.

Example 2

This example includes the elements of example 1 wherein R₁, R₂ and R₃ are selected from the group consisting of alkyls selected from methyl, ethyl and/or propyl groups.

Example 3

This example includes the elements of example 1 wherein R₁, R₂ and R₃ are methyl groups.

Example 4

This example includes the elements of example 1 wherein R₁, R₂ and R₃ are selected from methyl and ethyl groups.

Example 5

This example includes the elements of example 1 wherein the compound indicates a vapor pressure of 0.1 Torr to 1.0 Torr over the temperature range 95° C. to 130° C.

Example 6

This example includes the elements of example 1 wherein the compound has a melting point of 67.2° C., plus or minus 5° C.

Example 7

According to this example there is provided a process for forming a film comprising

-   -   (a) exposing a heated surface to the vapor of the following         compound:

wherein R₁, R₂ and R₃ are selected from the group consisting of alkyls, allyls, aryls, heteroaryls, hydrogen, non-metals and metalloids and where R₁, R₂ and R₃ are different or the same;

-   -   (b) exposing the substrate to a co-reactant; and     -   (c) forming a film on the surface of said substrate wherein said         film includes Sc₂O₃ or Sc₂S₃.

Example 8

This example includes the elements of example 7 wherein R₁, R₂ and R₃ are selected from the group consisting of alkyls selected from methyl, ethyl and/or propyl groups.

Example 9

This example includes the elements of example 7 wherein R₁, R₂ and R₃ are methyl groups.

Example 10

This example includes the elements of example 7 wherein R₁, R₂ and R₃ are selected from methyl and ethyl groups.

Example 11

This example includes the elements of example 7 wherein the film has a thickness of 10 Angstroms to 300 Angstroms.

Example 12

This example includes the elements of example 7 wherein the compound indicates a vapor pressure of 0.1 Torr to 1.0 Torr over the temperature range 95° C. to 130° C.

Example 13

This example includes the elements of example 7 wherein the compound has a melting point of 67.2° C., plus or minus 5° C.

Example 14

This example includes the elements of example 7 wherein the co-reactant comprises water.

Example 15

This example includes the elements of example 7 wherein the co-reactant comprises hydrogen sulfide (H₂S).

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications are possible within the scope of the claims. Accordingly, the claims are intended to cover all such equivalents. 

The invention claimed is:
 1. A compound having the structural formula:

wherein R₂ and R₃ are selected from the group consisting of alkyls, allyls, aryls, heteroaryls, hydrogen, non-metals and metalloids, wherein R₁ is selected from the group consisting of allyls, aryls, heteroaryls, hydrogen, non-metals and metalloids, and wherein R3 is a group different from an R1—CH₂— group.
 2. The compound of claim 1 wherein R₂ and R₃ are selected from the group consisting of alkyls selected from methyl, ethyl or propyl groups.
 3. The compound of claim 1 wherein R₂ and R₃ are methyl groups.
 4. The compound of claim 1 wherein R₂ and R₃ are selected from methyl or ethyl groups.
 5. The compound of claim 1 wherein said compound indicates a vapor pressure of 0.1 Torr to 1.0 Torr over the temperature range 95° C. to 130° C.
 6. The compound of claim 1 having a melting point of 67.2° C., plus or minus 5° C. 